This application seeks support for a project of research directed toward better understanding of the molecular mechanisms and cellular functions of chloride transport across human red blood cell membranes. Our investigation of the molecular mechansim of anion transport seeks to solve four major unsolved problems: first, the isolation and identification of the components of the erythrocyte membrane responsible for and controlling chloride transport; second, the mechanisms by which these components may be reincorporated into model lipid membrane systems; third, the factors involved in the kinetic behavior of these reconstituted anion transport systems; fourth, the physical-chemical parameters of the purified membrane components. Experiments designed to answer questions relevant to these problems involve observations under various conditions of solubilization and separation of membrane proteins, electrical properties of thin lipid bilayers, surface tension and potential of monolayers, calorimetry of proteins and lipids, electrokinetic properties of vesicles, fluxes of tracer ions across liposomes, red cell ghosts and bilayer membranes.